Mapping the perturbation potential of metallic and dipolar tips in tunneling spectroscopy on MoS${}_2$

Abstract

Scanning tunneling spectroscopy requires the application of a potential difference between the sample and a tip. In metal-vacuum-metal junctions, one can safely assume that the potential is constant along the metallic substrate. Here, we show that the inhomogeneous shape of the electric potential has to be taken into account when probing spatially extended molecules on a decoupling layer. To this end, oligothiophene-based molecules were deposited on a monolayer of molybdenum disulfide (MoS${}_2$) on a Au(111) surface. By probing the delocalized molecular orbital along the thiophene-backbone, we found an apparent intramolecular shift of the positive ion resonance, which can be ascribed to a perturbation potential caused by the tip. Using a simple model for the electrostatic landscape, we show that such a perturbation is caused by the inhomogeneity of the applied bias potential in the junction and may be further modified by an electric dipole of a functionalized tip. The two effects can be disentangled in tunneling spectra by probing the apparent energy shift of vibronic resonances along the molecular backbone. We suggest that extended molecules on MoS${}_2$ can be used as a sensor for the shape of the electrostatic potential of arbitrary tips.

References in corpus (5)

• Tuning a Circular p-n Junction in Graphene from Quantum Confinement to Optical Guiding
• Scanning Quantum Dot Microscopy
• Gating the charge state of a single molecule by local electric fields
• Investigating Atomic Contrast in Atomic Force Microscopy and Kelvin Probe Force Microscopy on Ionic Systems using Functionalized Tips
• Moiré structure of MoS${}_2$ on Au(111): Local structural and electronic properties

Cited by in corpus (4)

• Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope
• Vibrational excitation mechanism in tunneling spectroscopy beyond the Franck-Condon model
• Monolayers of MoS${}_2$ on Ag(111) as decoupling layers for organic molecules: resolution of electronic and vibronic states of TCNQ
• Influence of atomic-scale defects on coherent phonon excitations by THz near fields in an STM